Novel pregelatinized starches and process for preparing same

ABSTRACT

Pregelatinized starches are prepared by pasting an aqueous slurry of a starch which contains at least 50 percent amylopectin at a temperature of at least 300* F, and then rapidly, preferably instantaneously, removing the water therefrom as by roll or spray drying. The resultant products rapidly disperse in water to form smooth pastes which are characterized by low initial viscosity and minimal setback.

United States Patent [72] Inventors Felix Joseph Germino 12414 83 rdAve., Palos Park, 111. 60464; Gerald Donald Miller, 3621 Douglas Road,Downers Grove, Ill. 60515; Jerry Adam Moskaluk, 14500 Sawyer Ave.,Midlothian,

in. 60445 Appl. No. 829,083 Filed May 29, 1969 Patented Sept. 21, 1971NOVEL PREGELATINIZED STARCHES AND PROCESS FOR PREPARING SAME 5 Claims,No Drawings [1.8. CI 127/32, 75/2, 127/69 Int. Cl C131 1/08 Field ofSearch 127/28, 32, 69, 70, 71

OTHER REFERENCES Ward Pigman, ed., The Carbohydrates," 676, AcademicPress, New York, 1957.

Primary ExaminerMorris O. Wolk Assistant Examiner-Sidney MarantzAttorneys Frank E. Robbins, Janet E. Price, Robert D.

Weist, Martha A. Michaels and Dorothy R. Thumler ABSTRACT:Pregelatinized starches are prepared by pasting an aqueous slurry of astarch which contains at least 50 percent amylopectin at a temperatureof at least 300 F, and then rapidly, preferably instantaneously,removing the water therefrom as by roll or spray drying. The resultantproducts rapidly disperse in water to form smooth pastes which arecharacterized by low initial viscosity and minimal setback.

NOVEL PREGELATINIZED STARCHES AND PROCESS FOR PREPARING SAME Thisinvention relates to cold water dispersible starch products and to amethod for preparing same.

So-called pregelatinized starches, i.e. starches which have beengelatinized and dried and which will disperse when added to cold waterto form pastes, have long been known to the art. They are generallyprepared either by first gelatinizing an aqueous slurry of starch, as byheating it to its gelatinization temperature, and then instantaneouslyremoving the moisture, as by means of a roll or spray drier, or,alternatively, by passing an aqueous slurry of granular (i.e.ungelatinized) starch through a suitable apparatus, e.g. a roll or spraydrier, wherein the starch is simultaneously gelatinized and dried.

When an ordinary (i.e. unmodified and underivatized) starch is subjectedto a conventional pregelatinizing treatment the product will, uponaddition to cold (i.e. room temperature) water, form a smooth,relatively viscous paste. For certain applications, pregelatinizedstarches which will form pastes of low viscosity are desirable; suchproducts are customarily prepared by hydrolyzing the starch, as withacid or enzyme, prior to or simultaneously with the pregelatinizingtreatment. Hydrolysis causes molecular degradation of the starch, thatis to say, it breaks down the starch molecules; because of this theresultant pastes are not only low in viscosity but low in molecularweight as well.

Another feature of pastes prepared from ordinary pregelatinized starchis their tendency to increase in viscosity upon standing; thischaracteristic is generally referred to as setback." conventionally,setback is minimized by derivatizing the starch, i.e. adding substituentgroups to the molecule.

We have discovered a simple, rapid, and inexpensive method for preparingpregelatinized starches having the ability to disperse rapidly in coldwater to form exceptionally smooth pastes, which pastes arecharacterized by low initial viscosity and exceptionally good viscositystability (i.e. minimal setback). Furthermore, unlike conventionalpregelatinized starches which have been subjected to hydrolysis to lowertheir paste viscosity, the starches of our invention are characterizedby substantially no, or at most very slight, molecular degradation.

It is an object of the present invention to prepare cold waterdispersible starches which will reconstitute to form pastes having lowinitial viscosity and minimal setback.

Another object is to prepare pregelatinized starches which will rapidlydisperse in cold or warm water to form exceptionally smooth pastes oflow viscosity.

An additional object is to treat starch in such a way that the moleculesof same will be substantially undegraded, but pastes of the starch willnevertheless exhibit low viscosity and exceptionally good viscositystability.

Other objects and advantages will be apparent from the specification andthe appended claims.

Briefly, the process is as follows. A granular starch which contains atleast 50 percent amylopectin is slurried in water and pasted at atemperature of at least about 300 F., after which the water isinstantaneously removed.

The starch can be any starch provided it contains at least about 50percent amylopectin. Cereal starches, such as those derived from corn,wheat, barley, etc.; tuber starches, such as those obtained frompotatoes, tapioca, or the like; and the waxy starches," e.g. waxy maize,waxy rice, and waxy sorghum, which consist entirely or substantiallyentirely of amylopectin, and are all suitable for the practice of theinvention. The high amylose" starches, i.e. those which contain 60percent amylose or more, as well as amylose itself, are not suitable, inthat these starches produce products which form gels upon reconstitutionwith water, and gel formation is an undesirable characteristic in theapplications for which the products of the invention find their greatestutility. The starches can be modified and/or derivatized prior to thepasting treatment. The only critical requirements for starches to betreated in accordance with the invention are (1) they must be granular,i.e. ungelatinized, (2) they must be capable of being gelatinized inwater (for example, a starch which is so highly cross-linked that itwill not undergo gelatinization could not be used), and (3) they mustcontain at least 50 percent amylopectin.

The instantaneous removal of the water after the high temperaturepasting can be performed in any suitable apparatus, e.g. a drum drier, aspray drier, a belt drier, a foam mat drier, or the like, the onlyrequirement being that the apparatus be capable of drying the starchpaste very rapidly.

The original slurry can contain up to about 35 percent starch solids (byweight, based on the weight of the total slurry). As stated before, thestarch must be pasted at a temperature of at least about 300 F. The onlyupper temperature limit is that at which substantial moleculardegradation of the starch will take place, e.g. over about 450 F.Temperatures of from about 315 F. to about 360 F. are preferred.

It is very important that the paste not be permitted to cool to a pointat which the starch begins to retrograde or becomes aggregated prior toremoval of the water. The temperature at which retrogradation oraggregation begins depends upon the solids content of the paste. Forexample, a 35 percent solids paste will begin to retrograde at about 190F., while one of 12 percent solids will begin to retrograde at about-l50 F. Also, it is preferred that the paste be fed to the drier veryquickly after the completion of the pasting step, because the longer itis held at a high temperature the greater is the likelihood of moleculardegradation an-d/or crystallization.

The products, because of their ability to reconstitute in cold water toform smooth pastes of relatively low viscosity, high molecular weightand minimal setback, are extremely useful as adhesives and as coatingsand sizings for paper and textiles. It has also been observed that thereconstituted pastes have excellent film-forming properties, i.e., theywill readily form films which exhibit excellent oil holdout and waterholdout properties. The products are also excellent iron oxidedepressants in the calcium soap flotation process for concentrating ironores.

Structurally, the products of the invention are characterized bycomplete granular fragmentation, as contrasted with the conventionalpregelatinized starches which contain a certain amount, usually about10-15 percent, of intact granules.

The following examples will illustrate the practice of the invention.They are intended for illustrative purposes only, and should not beconstrued as limiting the scope of the invention in any way.

EXAMPLE I A series of runs was made in which aqueous slurries, at 25percent solids concentration by weight, of regular, unmodified cornstarch were heated in a steam injection cooker to temperatures of from212 F. to 355 F. until they were completely pasted. Immediately afterpasting the products were passed over a 24 inch roll drier, operated at2.6 rpm. and 100 lbs.

steam, the skin temperature of the rolls being 284 F. The

TABLE 1 Brooktield vis- Concentration Brookfield viscosity of reconolreconstituted cosity of reconstitutod pastes Pasting temp., pastes,weight stituted pastes after 24 hours at F. percent atF., cps. 150 F.,cps.

Approximately.

As can be seen from Table l, pastes of starches prepared in accordancewith the invention (cooked at temperatures of 300 F. and 355 F.) weresubstantially lower than those cooked at 212 F. and 250 F.

Blender at 4,000 r.p.m. prior to addition to the pulp. ln run 5 thealkaline starch dispersion was cooked at 100 C. for minutes prior toaddition to the pulp.

Table ll sets forth the amounts of starch used in each run As can alsobe seen from the table, pastes of starches 5 (calculated on the basis ofpounds of starch per ton of ore), prepared in accordance with theinvention which were held and the analyses of the froth and concentrateportions of each for 24 hours increased only slightly in viscosity. r

IABLE 11 Percent Lb. starch Percent Percent Fe re- Run No. Corn starchused per ton ore Product weight Fe covery 1 Prepared according tolnvention- 3 Froth 25. 94 33. 65 15.93 Concentrate 74. ()6 62. 21 84. U7

2 Regular. 3 Frotli 51. 00 47. 75 44. 21 Concentrate. 4U. 00 62.71 55.79

3 Regular 4 Froth 23. 90 30. 40 13. 23 Concentrate. 76. 10 62. 64 86. 77

4 Homogenlzed regular 3 Froth 21. 7O 28. 19 11. 24 Concentrate. 78. 306'2. 31 88. 76

5 Cooked regular 3 Froth 48. 72 46.73 41. 39 Concentrate- 51. 28 62. 8858. 61

EXAMPLE II An aqueous slurry at 25 percent solids of white milo starch25 was pasted at 3350 F in a Steam injection cooker and from the percentiron recovery in the concentrates, ll. 18 mediately roll dried as inExample 1. The product was added to f P at 3 SFarch per ton of ore thestarch of the at a of 26 percent sohds; the starfzh re.adlly dlspflsedto form a smooth 30 $112! has been subjected to extensive shearing in ablender or as paste The Brookfield vlscosny (at 20 'h 7200 regularstarch used at the increased rate of 4 lbs. per ton. Ad-

EXAMPLE I" vantages in the use of starch prepared in accordance with theinvention are that less of it needs to be used as a depressant A 16percent aqueous slurry of regular unmodified corn and that itsdispersions do not need to be sheared extensively starch was pasted at360 F. in a Votator indirect heat to be obtained in a useful form.exchanger. Immediately after pasting the product was dried in While theinvention has been described in connection with a spray drier. A 25percent solids paste was prepared in water specific embodiments thereof,it will be understood that it is at 110 F. The Brookfield viscosity ofthe paste was l26,000 capable of further modification, and thisapplication is inc.p.s. tended to cover any variations, uses, oradaptations of the in- Th example was repeated using wheat h, waxy i 40vention following, in general, the principles of the invention starchand potato starch with comparable results. In all cases and ing suchdepartures from the present disclosure as the products rapidly dispersedin water to form smooth pastes come within known customal'y Practice inthe to which which were characterized by low initial viscosity andminimal the invention pertains and as y be pp the essemial Setbackfeatures hereinbefore set forth, and as fall within the scope of theinvention. EXAMPLE lV What is claimed is: This example illustrates theuse of starch prepared in ac- Process for preparmga-prefgelanmzed Cvoldwater dlsper' slble starch product comprising. cordance with theinvention in the concentration of lron ores. L heating an aqueous slurryf a granular r h, said granu- S tandard procedure for ore flotanon a larstarch containing at least 50 percent amylopectin, at a descnpilonofwhlch was emPloyed temperature of at least about 300 F. for a timesufficient A 500-gram sample of iron ore lS pulped to 30 percent topaste completely Said Starchand solids in a batch laboratoryconditioner. To this ls added a 2 thereafter rapidly removingsubstantially all of the percent starch dispersion prepared by stirringthe starch in 0.5 moisture from the pasted starch N sodium hydroxidesolution for 30 mlnutesat room tempera- 2. process of claim {wherein themoisture is removed by ture. The pH of the pulp and starch mixture is adusted to 1 1.8 roll-drying the pasted starch. and the pulp isconditioned for 2 minutes. This is followed by process f claim 1 whereinthe moisture is removed by 1-minute conditioning with calcium chloride(2 lbs. per ton Spray drying the pasted starch.

Ore) h 2 minutes Conditioning with Actihol FAQ 4. Process of claim 1wherein said starch slurry is heated at a P The Conditioned P p istransferred to Fager- 6o temperaturewithin the range of between about315 F. and gren laboratory flotation machine, diluted to 20 percentabout 360 F solids, and floated for 5 minutes. The froth and the concen-5, A l i i d Starch product hi h ill idl Irate are Weighed and yzfOrifOn Content disperse in water to form a smooth paste having lowinitial Five runs were made, employing different starches asfolviscosity and excellent viscosity stability, said starch being lows.Run 01 used a corn starch treated in accordance with furthercharacterized by complete granular fragmentation and Example I, pastedat 340 F. Runs 2 and 3 employed regular, substantially no moleculardegradation, said starch having unmodified corn starch in two differentamounts. ln run 4 been prepared in accordance with the process ofclaim 1. regular unmodified corn starch was used, and the alkalinestarch dispersion was homogenized for 5 minutes in a Waring

2. thereafter rapidly removing substantially all of the moisture fromthe pasted starch.
 2. Process of claim 1 wherein the moisture is removedby roll-drying the pasted starch.
 3. Process of claim 1 wherein themoisture is removed by spray drying the pasted starch.
 4. Process ofclaim 1 wherein said starch slurry is heated at a temperature within therange of between about 315* F. and about 360* F.
 5. A pregelatinizedstarch product which will rapidly disperse in water to form a smoothpaste having low initial viscosity and excellent viscosity stability,said starch being further characterized by complete granularfragmentation and substantially no molecular degradation, said starchhaving been prepared in accordance with the process of claim 1.